The present invention relates to a photometric device. It is used in the measurement of the optical density of fluids (for example liquids) and in particular in the measurement of the turbidity of the waters of rivers or nuclear reactors, as well as for the detection of pollutants in liquids or gases.
Photometers are known which comprise a cell containing a volume of fluid to be analysed and optical means for making a light beam pass through said cell. The measurement of the attenuation due to the passage through the vessel makes it possible to calculate the optical density of the fluid and the concentration of one of the substances present in the fluid.
Although such photometers are suitable in certain cases, they have the disadvantage of offering the light beam only a short path which limits their precision. Therefore, photometers have been proposed which have two generally plane mirrors disposed on either side of the vessel in such a way that the light beam can pass to and fro between the mirrors, the optical path being lengthened for the same overall dimensions.